The epithelium of the rabbit cornea has been shown to possess an inward (tears to stroma) sodium transport system and an outward cyclic AMP-dependent chloride transport system. In vitro measurements of both sodium and chloride fluxes will be made at open circuit to determine the directionality of solute movement. These findings will be correlated with measurements of epithelial and stromal volume changes under a variety of conditions to determine the relationship of each transport system to volume control. Microelectrodes will be used to further explore the membrane origin of corneal potential and transport and to evaluate the relative ionic conductance of intracellular versus extracellular pathways. This approach is to be supplemented through the flux measurement of cell membrane impermeable solutes, electron microscopy and electron probe analysis. The effect of agents which are found to modify membrane permeability will be studied with the objective of improving drug penetration.